1. Field of the Invention
The present invention relates to a cooling system used for a hybrid-powered automobile which is driven by a combination of a water-cooled engine and an electric motor.
2. Description of the Related Art
The cooling system used for a hybrid-powered automobile includes: a radiator for engine use which cools an engine; and a radiator for electric parts use which cools electric parts such as an inverter and also cools an electric motor. In some cases, the cooling system used for a hybrid-powered automobile further includes a condenser which cools the gas-phase refrigerant, at a high temperature, flowing in an air-conditioner.
In the case where the above three heat exchangers are provided in the cooling system used for a hybrid-powered automobile, the radiator for cooling electric parts, the condenser for cooling the gas-phase refrigerant and the radiator for cooling the engine are arranged in series in this order in the flow of air, that is, a so-called three row mounting type cooling system is put into practical use.
There is also a cooling system in which the radiator for cooling the engine and the radiator for cooling electric parts are arranged on the same plane, that is, the radiator for cooling the engine and the radiator for cooling electric parts are arranged in parallel with each other with respect to the air flow direction. For example, this cooling system is disclosed in the official gazette of JP-A-10-259721. In the case where the three heat exchangers are provided, the cooling system has been put into practical use in which the radiator for-cooling the engine and the radiator for cooling electric parts are arranged on the same plane and the condenser is arranged on the upstream side of the air flow with respect to the radiator for cooling the engine and the radiator for cooling electric parts.
However, in the case of the above three row mounting type cooling system, the length of the cooling system is extended in the longitudinal direction of the vehicle. Therefore, problems are caused when the three row mounting type cooling system is mounted on the vehicle.
In this connection, in order to cool electric parts, such as an inverter circuit, to an appropriate temperature, it is necessary to maintain the temperature of cooling water circulating in the radiator for cooling the electric parts at about 60° C. The temperature of the refrigerant in the condenser is approximately 70° C., and the temperature of the cooling water in the radiator for cooling the engine is approximately 100° C. In other words, the cooling water temperature of the radiator for cooling the electric parts is substantially the same as the refrigerant temperature of the condenser. Due to the foregoing, the following problems may be encountered.
In the case of the three row mounting type cooling system in which the condenser is arranged on the downstream side of the air flow of the radiator for cooling the electric parts, as heat is radiated from the radiator for cooling the electric parts, the air temperature at the inlet of the condenser is raised, and a temperature difference between the air and the refrigerant is reduced. Therefore, it becomes impossible for the condenser to exhibit a necessary cooling performance.
On the other hand, in the case where the radiator for engine use and the radiator for electric parts use are arranged on the same plane, the air temperature at the inlet of the radiator for electric parts use is raised by the heat radiated from the condenser, and a temperature difference between the air and the cooling water is reduced. Therefore, it becomes impossible for the radiator for electric parts use to exhibit a necessary cooling performance.
When the inverter capacity is enhanced in order to increase an output of the hybrid-powered automobile, the radiator for the electric parts use is made larger in size according to an increase in the required capacity. In the case where the radiator for engine use and the radiator for electric parts use are arranged on the same plane, it becomes necessary to reduce the size of the radiator for engine use to correspond to an increase in the size of the radiator for electric parts use. Accordingly, the following problem may be encountered. A quantity of heat to be radiated from the radiator for engine use becomes insufficient.